Diminished Seventh Chords
The four basic chord types (also referred as triads) are major, minor, diminished and augmented. They all contain a root note, third and fifth. All the chords studied so far are based upon major or minor chords. A diminished chord (o) has the formula 1 b3 b5. The diminished seventh chord is generally used instead of the basic diminished chord by adding a double flattened seventh to the diminished triad.
The diminished seventh chord consists of four notes taken from the major scale of the same letter name. These notes are the first (1), flattened third (b3), flattened fifth (b5) and double flattened seventh (bb7) notes of the major scale, so the chord formula for the diminished seventh chord is:
The G Diminished Seventh Chord (Gdim)
Although the correct name is diminished seventh, it is commonly referred to as a diminished chord (although technically incorrect). When reading sheet music you can play a diminished seven chord (o7) when you see the diminished (o) chord symbol.
Double flat ( bb ) means to lower the note pitch by one tone (2 fret on the bass guitar).
The following diagrams show two common arpeggio patterns for a diminished chord. Both of these patterns are the same diminished chords.
G Diminished Seventh Arpeggio Pattern
As the diminished seventh arpeggio consists entirely from consecutive minor 3rds piled on top of each other;
E.g., the notes of the Go are G, Bb, Db and Fb,
G - Bb = min 3rd,
Bb - Db = min 3rd,
Db - Fb = min 3rd,
Fb - G = min 3rd etc. all inversions have the same pattern.
The diminished seventh chord arpeggio actually has four different names. To understand why this is so examine the formula for a diminished seventh chord, 1 b3 b5 bb7. By applying this formula to the respective scales of each note in the chord, it may be seen that Go7, Bbo7, Dbo7 and Eo7 all contain the same notes, thus the same arpeggio may be used for all four chords.
The previous two chord arpeggios can be called either Go7, Bbo7, Dbo7 or Eo7.
The following table illustrates this point by showing that the notes in each chord are the same.
Dbo7, can also be called C#o7, Bbo7 can also be called A#o7.
As each arpeggio represents four different dim7 chords, all the diminished seven chords can be covered in just three frets. The next example refers to the 4th string.
The diminished 7 chord on the 4th fret is the same as the diminished 7 chord at the 1st fret etc.
The easiest way to remember the names of the diminished 7 chord is simply to read off the notes contained in the chord. Conversely if you wish to find a particular diminished chord all you need to do is find that note on the fretboard and form the chord arpeggio around it.
Example 135 uses the diminished seventh arpeggio pattern throughout over two octaves.
Example 136 uses the diminished seventh arpeggio pattern A + B combined.
